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La plataforma permanente Atomium Culture reúne a las universidades, periódicos y empresas más prestigiosos de Europa para promover el flujo del conocimiento más allá de fronteras, entre sectores y hacia el público en general.

Tree-Like Molecules for a Solar Future

Por: | 09 de abril de 2013

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Humankind is facing energy and climate crises because of the massive consumption of fossil fuels such as oil. Fossil fuels are formed when solar energy is converted by natural photosynthesis and trapped in the Earth’s crust over a long period of time. Oil is a densely packed energy source that is easily transported and stored; characteristics that allow consumption abuse. However, humankind is now being forced to change consumption patterns because of climate problems and shortages of oil resource. Among the alternative energy sources, the Sun is very promising since more solar energy strikes Earth in one hour than all of the energy consumed by all humans in an entire year. With that availability, what is the problem? One aspect of the problem is that the Sun’s energy is very diluted and intermittent. To tap the potential of solar energy, we need to convert that energy into heat, electricity, and fuels. Heat production is the easiest as it can be obtained by using solar thermal panels, but the heat cannot be transported or stored. Electricity can be produced by photovoltaic cells, is easy to transport, but difficult to accumulate. Solar-source fuels are the most desirable way to tap solar energy as they combine both positive features—transport and accumulation. As usual, the most desirable is also the most difficult to achieve.

Tree-like molecules, called dendrimers from the Greek word dendron (tree), can improve the efficiency of conversion of solar energy to electricity or to chemical energy (solar fuel). Dendrimers are like trees in which you can have different kinds of “fruits” in different positions on the branches. Dendrimers are ideal candidates for organizing the component units (“fruits”) in the dimensions of space, time, and energy to maximize the efficiency of the light-harvesting process. In a dendrimer as shown in the illustration, the multicolored fruits can absorb the whole solar spectrum and transport that energy to the root area. During my research, I studied several dendrimers that perform as molecular antennae and established a practical design basis for an efficient molecular antenna. The challenge is the integration of these systems in photovoltaic devices in order to capture all the energy coming from the sun.


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Taking inspiration from Nature, we can use tree-like molecules for artificial photosynthesis. Green plants harvest solar light by using molecular antenna systems consisting of pigment–protein complexes and they use the obtained energy to convert low-cost, low-energy-content materials (water and carbon dioxide) into dioxygen (O2) and high-energy-content materials which, ultimately, are used to produce a fruit. The dendrimers being studied do not need to produce the color, shape, and perfume of an apple; they only need to produce a fuel; nonetheless, a very challenging task.

A possible route is to convert an abundant, inexpensive material like water into molecular oxygen and molecular hydrogen, which can then be converted back to water, in the process producing energy without associated pollutants. However, water is transparent, so it will not absorb light. To convert water into hydrogen (H2) and oxygen (O2) by solar light absorption, as illustrated above, a molecular antenna that is coupled to a reaction center and to catalysts can be used. In that approach, the absorbed energy is used to separate molecular charges, which are then accumulated by catalysts and used for water splitting. To reach this ambitious goal, current research involves many competences and specialists from different disciplines; a very pleasant and stimulating aspect of the work.

Experiments need to be carefully designed and performed and results carefully analyzed and interpreted. Even so, scientists’ expectations are often disappointed. However, unexpected results which can be explained may be the most important and promising ones.

After a disappointing experiment in my post doctoral research, I found a sheet of paper on my desk with the sentence:

“If you got what you want you have made a measurement, but if you got what you did not want you have made a discovery”.

This was left by my supervisor, and was appropriate as we obtained a very interesting result out of that experiment. Similarly, the famous scientist Albert Szent-Gyorgyi said:

Discoveries consist in seeing what everybody has seen and thinking what nobody has thought”.

I suggest that funding agencies and governments keep such comments in mind when deciding to fund only what appears to be very applicative research so as to be sure of obtaining a profit from the invested money. In many cases, there will be only a technological improvement, not a scientific breakthrough.

Paola Ceroni
University of Bologna

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